Conventionally, a lancing device of this kind is disclosed in the Japanese Patent Laid-Open No. 11-9577 for example. The lancing device disclosed in this gazette includes, as shown in FIG. 31 of this application, a generally tubular housing 90 and a lancet holder 92 holding a lancet L. The housing 90 has an end fitted with a tubular plunger 93 having a check valve 91. Though details will not be described here, according to this lancing device, when the plunger 93 is pushed in a direction shown by an arrow Na, the lancet holder 92 latched at a predetermined place in the housing 90 is forced to unlatch. Thus, the lancet holder 92 is propelled forward by an elastic force from a spring 95 toward an open front end 90a of the housing 90. Though not illustrated, the front end of the housing 90 is pressed onto the skin, and therefore the forward movement of the lancet holder 92 drives the tip of the lancet L into the skin.
Once the lancet holder 92 has moved forward, the lancet holder 92 is returned by an elastic force from a return spring 94. Likewise, the plunger 93 is moved back to its original position by an elastic force from a spring 96. This causes a volume increase in a space 97 in the plunger 93, creating a vacuum in the housing 90. A vacuum can also be created in the housing 90 by returning action of members 98a, 98b. Therefore, if the front end of the housing 90 is still pressed on the skin, the skin comes under the vacuum, and bleeding is promoted from the place pricked by the lancet L. The check valve 91 closes when the plunger 93 returns, thereby helping the generation of the vacuum, and opens when the plunger 93 is moved forward, to help smoothen the forward movement of the plunger 93.
However, the conventional lancing device has following drawbacks.
Specifically, there is personal difference in the volume of bleeding from the place pricked by the lancet L. Also, the same person bleeds differently from place to place; some place bleed easily while some others do not. However, conventionally, the level of vacuum created in the housing 90 is more or less the same all the time. Therefore, from time to time depending on the vacuum in the housing 90, it is not possible to obtain a sufficient amount of bleeding, or the lancing causes too much bleeding.
Another problem is that conventionally, the vacuum can be created in the housing 90 only after the lancet L has been shot to the skin. On the other hand, when lancing is to be made on a thin and easily relaxing part of the skin for example, it is sometimes more preferable that the a vacuum should be created first to suck on the skin, before shooting the lancet L. However, this is not available in the convention, and has been an issue of inconvenience some times.
Further, users of lancing devices are often clinical patients or the aged who do not have physical or bodily advantages. Therefore, the devices should preferably be very easy to use.